api example code: hinton_demo.py

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#Initial idea from David Warde-Farley on the SciPy Cookbook
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.patches import Rectangle
from matplotlib.ticker import NullLocator
#from matplotlib.collections import RegularPolyCollection
#from matplotlib.colors import BoundaryNorm, ListedColormap

def hinton(W, maxWeight=None, ax=None):
    """
    Draws a Hinton diagram for visualizing a weight matrix.
    """
    if not ax:
        fig = plt.figure()
        ax = fig.add_subplot(1, 1, 1)

    if not maxWeight:
        maxWeight = 2**np.ceil(np.log(np.abs(W).max())/np.log(2))

    ax.patch.set_facecolor('gray')
    ax.set_aspect('equal', 'box')
    ax.xaxis.set_major_locator(NullLocator())
    ax.yaxis.set_major_locator(NullLocator())

    for (x,y),w in np.ndenumerate(W):
        if w > 0: color = 'white'
        else:     color = 'black'
        size = np.sqrt(np.abs(w))
        rect = Rectangle([x - size / 2, y - size / 2], size, size,
            facecolor=color, edgecolor=color)
        ax.add_patch(rect)
    ax.autoscale_view()

    # Reverse the yaxis limits
    ax.set_ylim(*ax.get_ylim()[::-1])

## Potential way using polygon collections that just has an issue with
## easily getting the squares scaled by the data.

#    height,width = W.shape
#    x = np.arange(width)
#    y = np.arange(height)
#    X,Y = np.meshgrid(x, y)
#    xy = np.array([X.flatten(),Y.flatten()]).T
#    scaled_data = W.flatten() / maxWeight
#    cmap = ListedColormap(['black', 'white'])
#    norm = BoundaryNorm([-1., 0., 1.], cmap.N)

#    rect_col = RegularPolyCollection(4, rotation=np.pi/4,
#        sizes=np.abs(scaled_data) * 72 / ax.figure.get_dpi(), offsets=xy,
#        transOffset=ax.transData, norm=norm, cmap=cmap, edgecolor='none')
#    ax.add_collection(rect_col)
#    rect_col.set_array(scaled_data)
#    ax.autoscale_view()

if __name__ == '__main__':
    hinton(np.random.rand(20, 20) - 0.5)
    plt.title('Hinton Example')
    plt.show()

Keywords: python, matplotlib, pylab, example, codex (see Search examples)